1. Field of the Invention
The invention relates to an apparatus and a method for the low-contamination, automatic crushing of silicon fragments.
2. The Prior Art
Polycrystalline silicon (also known as polysilicon) is the starting material for the production of crystalline silicon for the electronics and solar industries. Most semiconductor components and solar cells are produced from crystalline silicon. Various crystallization processes, in which polysilicon is usually melted and then converted into monocrystalline or multicrystalline silicon by directional solidification, are used to produce crystalline silicon. Monocrystalline material is produced, for example, by the Czochralski (CZ) process, while multicrystalline material is produced by melting and directional solidification in the crucible or by pulling sheets or casting tapes. Monocrystalline silicon is the starting material for semiconductor components and solar cells. Multicrystalline silicon is used predominantly as starting material for solar cells.
Polysilicon is usually produced by vapor deposition in a reactor. This usually involves deposition of high-purity silane or chlorosilane on a hot substrate (preferably formed from silicon), so as to obtain solid ingots, blocks or boards. Before this polysilicon can be used in crystallization processes, it has to be comminuted. During this comminution, it is usually contaminated by abraded material in such a way that the contaminants on the surface have to be removed by cleaning processes.
It has only been possible to obtain polysilicon which is suitable for use in semiconductor or solar applications directly (i.e. without further cleaning), i.e. very pure polysilicon (total metallic contamination typically <10 ppba), by manual comminution. Consequently, the production of very small fragments is insufficiently productive and therefore uneconomical and, moreover, harmful to one's health. Known automatic crushing processes which are suitable for producing small crushed fragments either cause excessive surface contamination (e.g. standard jaw crushers, roll crushers, etc.), which requires complex subsequent purification, or are uneconomical on account of very complex machine designs or complex processes (see, for example, U.S. Pat. No. 5,464,159 (shock wave comminution), or U.S. Pat. No. 6,024,306 (comminution by current pulses) or U.S. Pat. No. 4,871,117 (preliminary thermal crushing; subsequent mechanical comminution) or European Patent No. EP 1 338 682 A2).